26 Invertebrate*. 



surface or else special areas of it ; sometimes a few of 

 these processes are rigid and act like little feet, or 

 else they are all equal and fine, invisible during their 

 active exercise owing to their rapid rate of motion. 



The outer layer of their body is a firm cuticle 

 which covers a differentiated protoplasmic lamina con- 



FIG. 14. 



Paramtzcium aurelia, an infusorian, showing the contractile vesicles (s\ 

 tndoplast (t\ oesophagus and mouth (o\ cilia and vacuoles. 



taining one or more clear spaces or contractile vesicles, 

 which when watched appear to expand and contract 

 regularly, pulsating like a heart, aerating the proto- 

 plasm. Within this layer is a more fluid mobile proto- 

 plasm containing granules, vacuoles and two peculiar 

 solid bodies called respectively endoplast or nucleus 

 and endoplastule. 



